This invention relates to an electronic sensing circuit which is responsive to a physical parameter such as pressure or displacement. In particular, it relates to an electronic sensing circuit which can be used in place of a linear variable differential transformer to provide sensor voltage outputs.
Linear variable differential transformers (LVDT's) are routinely used as physical sensing elements, for example, as pressure transducers or for measuring small displacements. As shown in FIGS. 1A and 1B, the LVDT 6 has a primary coil 4, secondary coils 8 and 10, and a movable core 14. A given reference voltage E is applied across the primary coil 4 from a voltage source 2. The secondary coils have equal windings and have output terminals 16, 18, 20. FIG. 1A shows the LVDT with the output terminals 20 of the secondary coils in common ground configuration with the primary coil, whereas FIG. 1B shows the output terminals in isolated configuration.
The core 14 is movable (indicated by the direction of the arrows) in response to a physical parameter, such as applied pressure or linkage to a component which undergoes small physical displacements. When the core 14 is symmetrically positioned between the two secondary coils, the output voltages V1 and V2 are equal. When the core 14 is displaced in either direction, the relation of the output voltages V1 and V2 changes correspondingly. Thus, the direction and amount of movement of the core 14 is indicated when V1 decreases relative to V2, and vice versa.
Although commonly used, LVDT's are subject to transducer failure and erroneous outputs, particularly in high vibration environments. The position of the core can be affected by vibrations and acceleration forces. It is therefore desirable to replace the LVDT in a sensing circuit with a sensing element that is less prone to transducer failure and erroneous outputs.